The present invention relates to a camshaft driving arrangement for a double overhead camshaft (DOHC) engine having two camshafts for opening and closing suction and exhaust valves at each of cylinder heads.
Japanese Patent Publication No. 59-74312 (=U.S. Pat. No. 4,553,473) discloses a camshaft driving arrangement of the prior art as shown in FIG. 5.
Referring to FIG. 5, there is shown a so-called V-type engine in which a cylinder block 1 includes two cylinder banks 1A and 1B angularly disposed to each other. One 1A of the tow cylinder banks has a plurality of cylinders displaced along the axis of a crankshaft 2 from a plurality of cylinders of the other bank 1B. There is provided a sprocket 3 at the end of the crankshaft 2 rotatably mounted to the cylinder block 1. Rotatably mounted to each of cylinder banks 1A and 1B are an intake camshaft 6 for opening and closing intake valves 5 and an exhaust camshaft 8 for opening and closing exhaust valves 7. Two idler gears 11 are rotatably mounted to the cylinder heads 4A and 4B, respectively. Each of the idler gears 11 has a large diameter gear 11A and a small diameter gear 11B. Fixedly mounted to the end of each of the camshafts 6 and 8 is a sprocket 9. Rotation of the crankshaft 2 is transmitted to the large gears 11A of the idler gears 11 through a rubber timing belt 10, causing rotation of the small gears 11B. Subsequently, the rotation of each of the small gears 11B is transmitted to the adjacent sprockets 9 through a chain 12. As a result, the intake camshafts 6 and the exhaust camshafts 8 are rotated synchronously, opening and closing the intake and exhaust valves 5 and 7. A tensioner 13 is used for adjusting the tension of the timing belt 10, and an idler gear 14 for stabilizing or ensuring an engagement of the timing belt 10.
According to this known camshaft driving arrangement, the timing belt 10 drivingly interconnects the sprocket 3 of the crankshaft 2, the large gears 11B of the idler gears 11 and runs through a running plane and this running plane is disposed axially outward with respect to the axis of the crankshaft 2 more than running planes of the two camshaft driving chains 12 are. The running planes of the two chains 12 are disposed in the common plane. This arrangement is disadvantageous in that the timing belt 10 has to be arranged outward the running planes of the camshaft driving chains 12, causing difficulty in reducing the axial dimension of the engine and in increasing assembling efficiency and maintenance efficiency of the idler gears 11 and chains 12.
An object of the present invention is to provide a camshaft driving arrangement which makes much contribution to reduced axial dimension of the engine and improved assembling and maintenance efficiency of idler gears and camshaft driving chains.